two parameters. The first comes from direct search for heavy
neutral gauge bosons at the Fermi Lab, which excludes a Z'
mass less than 600 GeV. The second limit comes from LEP
where
(1)
The research paper published by IJSER journal is about Signatures for Z'B-L Gauge Boson at Large Hadrons Collider using Monte Carlo Simulation Data 1
ISSN 2229-5518
Signatures for Z'B-L Gauge Boson at Large Hadrons
Collider using Monte Carlo Simulation Data
H.M.M.Mansour*
Department of Physics, Faculty of Science, Cairo University. mansourhesham@yahoo.com
* The author wishes to thank Mr. N. Bakhet for doing the numerical calculation.
Abstract— In the present work we search for Z'B-L heavy neutral boson in the dielectron events produced in proton-proton collisions at LHC using Monte Carlo simulation programs. To detect Z'B-L at LHC we used the data which are produced from pp collision of Pythia8 produced events at different energies for LHC then we use the angular distribution for the dielectron produced from Z'B-L decay channel's to detect the Z'B-L signal. B-L extension of the SM model predicts the existence of a Z'B-L heavy neutral massive boson at high energies and from our results which we had simulated for Z'B-L in theB-L extension of standard model we predict that aZ'B-L boson will be found at LHC and has a mass in the range from 1 TeV to 1.5 TeV.
Index Terms— Gauge bosons,Large hadron colliders,Monte carlo simulation,Z prime particles,cross sections,branching ratios,extended standard model.
—————————— ——————————
he fact that neutrinos are massive indicates that the Stan- dard Model (SM) requires extension. B-L model is an ex- tension for the SM which is based on the gauge group
In this section we present our results for simulation of Z' in
the B − L model using MC simulation. We first present pro-
GB-L=SU(3)C × SU(2)L × U(1)Y × U(1)B-L . The invariance of the
Lagrangian under this gauge symmetry implies the existence
of a new gauge boson (beyond the SM ones) and the sponta-
neous symmetry breaking in this model provides a natural
explanation for the presence of three right-handed neutrinos
in addition to an extra gauge boson and a new scalar Higgs.
Therefore, one can observe a very interesting phenomenology
which is different from the SM results and it can be tested at
the LHC. An extra neutral massive gauge boson correspond-
ing to B−L gauge symmetry is predicted. There are many models which contain extra gauge bosons. These models can be classified into two categories depending on whether or not they arise in a GUT scenario. In some of these models, the Z′
and the SM Z do not have true mass due to mixing. This mix- ing induces the couplings between the extra Z′ boson and the SM fermions .In our model of B−L extension of the SM, the extra Z′B-L boson and the SM fermions are coupled through the non-vanishing B−L quantum numbers. Searching for Z′B-L is accessible via a clean dilepton signal at LHC. We will simulate B − L extension of the SM, Which is based on the gauge group SU(3)C × SU(2)L × U(1)Y × U(1)B-L using MC programs at LHC and search for Z'B-L bosons in dielectron events pro- duced in pp collisions at different energies of LHC using the Monte Carlo event generator PYTHIA8 [1- 4] and the software tools (Data analysis ROOT package and ROOFIT package to fit any resulted histogram to get P.D.F. (Probability density func- tion)).Also we use MadGraph5/Madevent and CALCHEP programs. To identify the Z'B-L e+ e− signal, we use the di- electron angular distribution [5]. The leptonic decays Z'B-L ℓ+ℓ− provide the most distinctive signature for observing the Z'B-L signal at a Large Hadrons Collider. We will study the production of Z'B-L at LHC and the different branching ra- tios.Also; we will study Z'B-L using dielectron angular distribu- tion and analyze the results by using simulation event genera- tor PYTHIA8 and other software tools, ROOT and ROOFIT.
duction cross-sections of Z' at the LHC as a function of Z'
B-L B-L
mass for various g'' values (where g'' is the U (1)B-L gauge coupling constant) and for various energies for LHC, branch-
ing ratios as a function of Z B-L mass for heavy neutrino mass hv= 200 GeV which will have an effect on the different results of Z B-L due to it's heavy mass. We obtained different results in comparison with those reported in [6] where the analysis in this paper did not take into account the new heavy neutrino which is an important signature of the B-L model [7-9] .Also they did not give any branching ratio for heavy neutrino.
After that we give the result of Z B-L total width as a function of Z B-L mass for various values of g′'.
In figure 1 we present the production cross sections for Z'B-L for the most relevant production mechanisms. We can com- pare the production cross sections for different CM energies. Figure 1(a) gives the cross sections in the B − L model for Z'B-L at the LHC as a function of Z' mass for various g'' values (where g'' is the U (1)B-L gauge coupling constant) and energy of LHC = 14 TeV . Figure 2 (b) gives cross sections in the B − L model for Z' at the LHC for energies √s = 5, 7, 10, 12 and 14
TeV at fixed value of g''=0.2.At the patron level, the Z' pro- duction cross section depends on two main parameters the mass of Z' and the coupling constant g''. Therefore, the model B-L is controlled by two parameters: first, the mass of
the Z' second, the coupling constant g" determining Z'
B-L B-L
couplings.There are two experimental constraints on these
two parameters. The first comes from direct search for heavy
neutral gauge bosons at the Fermi Lab, which excludes a Z'
mass less than 600 GeV. The second limit comes from LEP
where
(1)
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The research paper published by IJSER journal is about Signatures for Z'B-L Gauge Boson at Large Hadrons Collider using Monte Carlo Simulation Data 2
ISSN 2229-5518
The extra neutral gauge boson Z'
B −L gauge symmetry breaking
acquires a mass due to the
Hadron Level: Hadronize=On, HadronLevel: Decay= On, Ha- dron Level: Bose Einstein=On
m2Z' = 4g''v'2 (2)
where g'' is the U(1)B-L gauge coupling constant and v' is the symmetry breaking scale
Table 1. B-L quantum number for different particles
particle | l | eR | νR | q |
YB-L | -1 | -1 | -1 | 1/3 |
Figure 2. Branching ratios for Z'B-L boson as a function
. of Z'B-L mass for heavy neutrino mass hv= 200 GeV .
From fig. 2, the branching ratios of Z'
for different quarks
are equal approximately and the branching ratios for different leptons are higher than those for the quarks and also the branching ratios for heavy neutrino (which have a mass200
GeV). In particular, BR (Z'
→ ℓ+ℓ−) varies between 17% and
17.5% where (ℓ = electron, muon, tau). But for heavy neutrino
BR (Z'
→ h h ) and for light neutrino BR (Z'
→ ν ν) they
B-L v v
B-L
vary between 8.5% and 9%. BR (Z'
→ qq) varies between
5.5% and 6%. Z'
can decay into one light and one heavy neu-
trino such a channel is highly suppressed by the correspond- ing (heavy-light) neutrino mixing and thus it can safely be neglected. Heavy neutrino is the most characteristic for B-L model so it affects other branching ratios because it has a mas- sive neutrino in comparison with the SM neutrino. From fig-
ure 2 we can search for Z'
at LHC via a clean dilepton signal
Figure 1. Cross-sections for Z'B-L as a function of Z'B-L
masses
which can be one of the first new physics signatures to be ob- served at the LHC. We will study Z'B-L in this paper by using
(a) For various g'' values and fixed value of LHC
the channel decay of Z'
to electrons pair using PYTHIA8 and
CM energy 14 TeV
(b) For various LHC CM energies and fixed value
of g''=0.2
The production cross sections for the Z'B-L signal in figure 1 are computed using MadGraph5 and PYTHIA8 where we generated the process pp --> ZB-L of B-L model using Mad-
turn off all other channels of decay of the Z'B-L particle where
the ratio of dielctron channel is the highest one and then use
these commands.
pythia.readString("900032:onMode=0"),
pythia.readString("900032:m0=1000")
pythia.readString("900032:onIfAll=11 -11")
where the first command turn off all decay channels of Z B-L
to 1000GeV and the
Graph5 and export this process to PHYTHIA8 then the main switches will stay on for Initial state Radiation(ISR) , Final State Radiation(FSR), FSRinResonances,and Decay. Hadroni- zation allows resonance decays and master switches for mul-
and the second one set the mass of Z'
third command permits the decay of Z'
tron only.
to electron and posi-
tiparton interactions stay on. PartonLevel: ISR= On, PartonLe- vel: FSR=On, PartonLevel: FSRin Process= On, PartonLevel: FSRin Resonances=On, Process Level: all = On, Process Level: resonance Decays=On, Parton Level: all=On, PartonLevel: Remnants=On, Parton Level: MPI=On, HadronLevel: all=On,
The Z' boson decays only to fermions at tree-level and its width is given by the following expression
(3)
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The research paper published by IJSER journal is about Signatures for Z'B-L Gauge Boson at Large Hadrons Collider using Monte Carlo Simulation Data 3
ISSN 2229-5518
where mf is the mass and Cf the number of colours of the fer- mion type f .In Figs. 3 and 4 we present the total decay width
By using dielectron angular distribution cos * where *
of the Z'
as a function of Z'
and g'', respectively where
is the angle in the dielectron rest reference frame between the
the other parameters were held fixed to three different values
negative electron and the incident incoming quark. PYTHIA8 gives only in Lab frame but we use * here which is in the
rest frame so we must convert from lab frame to rest frame to get * by using boost vector.
We define two additional reference frames:
(a) The colliding proton CM frame denoted by (this frame
is identical to the laboratory frame) and (b) The rest frame of the dilepton system denoted by *. The dilepton system is
boosted along the beam axis. The z-axis is chosen as the direc- tion of one of the beams, and it is then identical for and
* frames.It should be noted that there is a sign ambiguity in the measurement of cos *, since for a particular event, there is
no information about whether the incoming quark comes from the positive or negative z directions. Instead, it is useful to
consider the quantity cos ,where
is the angle between
Figure 3. Total width for Z'B-L boson as a function of g'' for different values of Z'B-L mass.
the dilepton system boost
the lepton direction [10]
(relative to the O frame) and
(5)
where the boost vector is
(6)
In order to obtain p l
the boost vector of the dilepton system
should be found and the transformation to the O* frame
should be performed
Figure 4. Total width for Z'B-L boson as a function of mass Z'B-L for fixed values of g''.
From figures 3 and 4 we see that the total width of a Z'
gauge boson varies from a few to hundreds of GeV over a
mass range of 1 TeV < Z'
< 5 TeV, depending on the value
of g''.
The decay widths of Z'
by:
→ ffbar in this model are then given
(4)
Figure 5. Angular distribution of dielectron of Z'B-L boson decay where forward electrons cos( *) >0 and- backward electrons cos( *) < 0.
Figures 3 and 4 are calculated by PYTHIA8 using the com- mands:
pythia.event[i].mWidth(), Parton Level: ISR=On, Parton Level: FSR=On.
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The research paper published by IJSER journal is about Signatures for Z'B-L Gauge Boson at Large Hadrons Collider using Monte Carlo Simulation Data 4
ISSN 2229-5518
In this work we have presented the LHC potential to discover
a heavy neutral massive gauge boson Z'
of the B-L exten-
sion of the SM model using MC programs where we have si- mulated the production cross section at different center of mass energies of LHC for various values of the coupling con-
stant g'' and branching ratios of Z'
to all different decay
channels to fermions. We presented the total width of Z' as
a function of Z'
mass. Also we presented the decay of Z'
into an electron–positron pair and we have presented dielec- tron angular distribution. All these signatures predict the exis-
tence of a new gauge boson Z'
at LHC.
It is a pleasure to thank T. Sjostrand, for useful discussions of PYTHIA, L. Basso and C. Duhr for useful discussions of B-L model and J. Alwall for useful discussions of MadGraph5/ MadEvent.
[1] T. Sjostrand, S. Mrenna, and P. Skands, J. High Energy Phys. 05 (2006) 026. [2] k T. Sjostrand , CERN-LCGAPP-2005-05 July 2005k
[3] T. Sjostrand,http://home.thep.lu.se/~torbjorn/php8160/Welcome.php.
[4] L. Basso, (PhD Thesis, university of southampton) ArXiv:1106.4462v1 [hep-ph] 22 Jun 2011
[5] L. Basso, (Master Thesis,Universit`a degli Studi di Padova,2007). [6] W. Emam, P Min´e 2008 J. Phys. G: Nucl. Part. Phys. 35 115008. [7] CDF Collaboration- arXiv:hep-ex/0602045v1 24 Feb 2006.
[8] L. Basso, arXiv:0903.4777 [hep-ph] 16 Sep 2009
[9] T.Sjostrand T, Eden P, Friberg C, Lonnblad L, Miu G, Mrenna S and
Norrbin Comput. Phys. Commun. 135 238.
[10] T. Sjostrand et al., Comput. Phys. Commun. 135, 238 (2001).
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